A zirconium silicate brick of the type described above is known from Schulle, "Feuerfeste Werkstoffe" ("Refractory Materials"), first edition, 1990, pp 220-224. For the production of sintered zirconium containing products naturally occurring zirconium silicate is used as a starting material. It is in theory chemically composed of two thirds zirconium dioxide and one third silicone dioxide. Under the influence of high temperatures in the order of 1700.degree. C. a decomposition occurs in the brick along with a distinct change of properties. Titanium dioxide furthers this decomposition. With the simultaneous presence of Al.sub.2 O, the decomposition begins at lower temperatures in the range of 1500.degree. C. Zirconium silicate products are formed by slip casting, stamping, but also by isostatic pressing, for which a fine grained starting powder is used. An additional binding phase usually is not necessary with these products. The contaminants, especially Al.sub.2 O.sub.3, TiO.sub.2, and Fe.sub.2 O.sub.3, should be kept to as small a fraction as possible, with the Al.sub.2 O.sub.3 being contained in a percentage of 0 5% to 10% the TiO.sub.2 &lt;0.1% and the Fe.sub.2 O.sub.3 &lt;0.5%. By this zirconium silicate refractories can be made that have a raw density between 4.2 g/cm.sup.3 up to about 4.5 g/cm.sup.3. Especially in glass troughs which are lined with such zirconium silicate bricks and which have temperatures of up to 1700.degree. C., do these bricks fulfill their functions due to the occurring decomposition only inadequately. In contact with the liquid glass of the melt corrosion occurs. The silicone dioxide is washed out and taken away, so that an erosion of the bricks results. The infiltration of Al.sub.2 O.sub.3 -constituents of the glass melt into the zirconium silicate brick and brings about a reaction with the SiO.sub.2. The result is the formation of mullite, which is connected with a decrease of the density and a volume expasion. This ultimately limits the service life of such zirconium silicate bricks.
From Verworner and Berndt, "Feuerfeste Baustoffe fur Glasschmelzanlagen" ("Refractory Materials for Glass Melting Facilities"), first edition 1977, pp 96-100, zirconium containing products are known and described therein, in which zirconium of high purity is used. The thermal dissociation is also described here, and the use of fine grained components is recommended. The fractions of contaminents are likewise fixed to a low level.
From the Shinagawa Techn. Report No. 25 (1981), pp 37-44 it is known to allow titanium dioxide not only in the form of natural contaminants of a fine grained starting powder with a fraction &lt;0.1%, but to add TiO.sub.2 in a comparably larger amount as a sinter-aiding means to the fine grained starting powder. By this zirconium silicate bricks of a slightly higher density and smaller porosity can be produced, which have a higher resistance against Al.sub.2 O.sub.3 diffusion from the glass melt. Several model experiments are reported herein, in which a fine grained starting powder is used with different grain sizes in the range of 300 .mu.m to 2 .mu.m or between 10 .mu.m and 2 .mu.m. Concerning the corrosion resistance, grain sizes between 44 .mu.m to 2 .mu.m are preferred.
It is the object of the invention to provide a zirconium silicate brick and a method for its production, which has a high corrosion resistance when used in glass melting facilities for boron silicate glasses and for which the described decomposition behavior at higher temperatures is reduced.